From: Planning the end of the world, well out to 2023!
A skate can glide over ice because there is a layer of ice molecules at the surface that are not as tightly bound as the molecules of the mass of ice beneath. These molecules are in a semiliquid state, providing lubrication. The molecules in this "quasi-fluid" or "water-like" layer are less mobile than liquid water, but are much more mobile than the molecules deeper in the ice. At about −250 °F (−157 °C) the slippery layer is one molecule thick; as the temperature increases the slippery layer becomes thicker.
It had long been believed that ice is slippery because the pressure of an object in contact with it causes a thin layer to melt. The hypothesis was that the blade of an ice skate, exerting pressure on the ice, melts a thin layer, providing lubrication between the ice and the blade. This explanation, called "pressure melting", originated in the 19th century. This, however, did not account for skating on ice temperatures lower than −3.5 °C, whereas skaters often skate on lower-temperature ice. In the 20th century, an alternative explanation, called "friction heating", was proposed, whereby friction of the material was causing the ice layer melting. However, this theory also failed to explain skating at low temperature. In fact, neither explanation explained why ice is slippery when standing still even at below-zero temperatures.
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